Endovascular brachytherapy is used for treatment of a wide variety of blood vessel lesions. An example thereof is the treatment of a vascular stenosis. A common treatment for a stenosis in a blood vessel is percutaneous translumenal angioplasty. The angioplasty is applicable to any blood vessel, but is very commonly carried out in connection with coronary blood vessels. Angioplasty is achieved by placing a catheter within the blood vessel near the stenosis and inflating a balloon on the catheter to cause compression of the stenosis and thus opening the occlusion. An ever present problem with such angioplasty is that of subsequent restenosis, and depending upon the particular angioplasty procedure and other factors, restenosis occurs on average in 33%, but maybe up to 45%, of all patients treated with angioplasty. The degree of restenosis varies, but restenosis can cause loss of lumen cross-sectional area such that the angioplasty is no longer successful and a further angioplasty or bypass surgery is required.
To retard or void such restenosis, in conjunction with angioplasty, a radioactive source is placed within the lesion and the lesion is radiated with certain dosages of radiation to retard or prevent restenosis.
Brachytherapy is also used to treat certain diseases, especially cancer, since the radiotherapy can be administered to very localized human body areas, as opposed to external beam radiotherapy. To achieve localized radiotherapy, a radioactive source is placed in close proximity to the tissue being treated.
In both of the above examples, the application of the radiotherapy is achieved by guiding a radioactive source through at least one radiation tube, until that source reaches the precise site of the tissue to be treated. A regimen of radiation is then administered according to a program defined for the particular tissue.
If radiation therapy, such as that exemplified above, were routinely administered to a number of patients, technicians administering the therapy would be unduly exposed to radiation hazard. To avoid such radiation hazard, apparatus has been developed for allowing the radiation source to be moved to the site of the radiotherapy while the technician is not in close proximity to the patients being treated, e.g. is not in the treatment room where the patient is being treated. Such apparatus is known in the art as remote afterloading apparatus for brachytherapy. When using such apparatus, a physician places a positioning member, e.g. a needle, canula or catheter (generically referred to as a radiation tube), at the site where the radiotherapy is to be effected. This radiation tube is attached at one end thereof to a connection head of the remote afterloading apparatus. After such positioning and connections are made, a technician can cause, e.g. from a remote location such as another room, the apparatus to drive a cable with a radioactive source attached at or near an end of the cable from a "safe" (a container for storing the radioactive source and shielding the radiation), through the remote afterloading apparatus, the radiation tube and to the site to be treated. Thus, a technician will not be in close proximity to the patients, e.g. will be in another room, while the radioactive source is out of the "safe" and while administering the therapy. Such apparatus and methods of operation are described in detail in U.S. Pat. Nos. 4,861,520; 4,881,937; 4,969,863; and 5,030,194.
Of course, it is important that the radioactive source be positioned precisely at the site of the tissue to be treated, and the afterloading apparatus usually provides means for determining the position of the source after it has passed through the afterloading apparatus and into the radiation tube. One form of such means of ensuring the correct position of the radioactive source is that of a stepping motor in the afterloading apparatus which drives a cable having the source at one end in very discrete and known steps. By use of an indexing means, the number of discrete and known steps required for the source to reach the site of treatment can be determined.
However, with afterloading machines which use a high dose rate radioactive gamma ray source, the precise position of that source in the patient cannot be determined by usual techniques of radiation, e.g. X-ray radiography or fluoroscopy device, since that high dose rate source would cause unacceptable doses of radiation to the radiation imaging system. To avoid the problem of unnecessary exposure, a "dummy" source having no radiation or very low levels of radiation is first threaded through the safe, afterloading apparatus and radiation tube to the site of the tissue to be treated. Since the dummy source does not present a radiation hazard, the exact position of that dummy source in the patient can be determined by the usual techniques of radiation, e.g. X-ray radiography and fluoroscopy device. The arrangement of such a dummy source is explained in detail in U.S. Pat. No. 5,030,194.
However, it is imperative that the technician very precisely determine the position of the radioactive source or the "dummy" (hereinafter simply "source" for conciseness purposes) and to very accurately determine the number of discrete steps of the stepping motor (or other equivalent drive apparatus) required for the particular arrangement of the radiation tube, etc., to ensure that the source has reached the precise site of tissue to be treated. This precise positioning of the source must be determined for each patient and each use of the afterloading apparatus for a patient, since the particular configurations of the flexible radiation tube, catheter, etc., can form different total lengths of travel from the afterloading apparatus to the site of radiation therapy due to the particular convolutions of the radiation tube, catheter, etc., for a specific application to a specific patient. If, for example, the radiation tube for a particular patient is configured in a substantial arc, the distance along that arc of travel for the source may well be significantly different from the travel of that source when that radiation tube is in a relatively straight configuration.
To further assist in very precise positioning of the source for irradiating a lesion, a catheter, used in the procedure, has markings thereon which are detectable by radiation, e.g. X-ray radiography or fluoroscopy device. These markings span the lesion, but those markings are not sufficiently precise for exactly positioning the source at the point of the lesion. In addition, the usual radiation tube of the afterloading apparatus is placed in a lumen of the catheter. In the case when it is placed in the catheter, it may also have such markings thereon. Accordingly, by using the stepping motor of the afterloading apparatus, the source can be placed within the markings, but it is still necessary to adjust the position of the source within those markings to the precise site of the lesion. Catheters, usually, are made of soft, flexible, supple materials which are relatively easily stretched, i.e. the length of a catheter, when inserted in the body of a patient, are, thus, not predetermined and fixed but may vary according to circumstances. The detailed description will exemplify a centering catheter with centering means in the form of one or more balloons or otherwise. It should be understood, however, that neither that centering means nor a centering catheter is required, and the present invention can be realized both with centering and with non-centering catheters and is independent of the kind of centering means used.
A centering catheter is a catheter provided with centering means for radially aligning the catheter with the blood vessel. Such centering means may comprise one or more inflatable balloons surrounding a central lumen. When the centering catheter is in a proper position, the balloon(s) are inflated. This causes the central lumen of the catheter to be centered in the lumen of the lesion such that when the source is placed within the centering catheter at the position of the lesion, it is centered within the lesion so that surrounding walls of the lesion receive equal radiation.
Heretofore, as noted above, the exact positioning of the source within the radiation tube disposed in the catheter is carried out by the technician by operating the stepping motor of the afterloading apparatus. The place (operating field) in which the procedure takes place may have a sterile area and a non-sterile area. The afterloading apparatus is not sterile and is consequently not disposed in the sterile area of the operating field. Thus, the physician in the sterile operating field must communicate with a technician operating the stepping motor for exact positioning of the source in the radiation tube and/or the catheter, and this leads to difficulties and lack of precision of source placement. Furthermore, physicians are accustomed to making minute movements of their tools happen manually. Even if the physician, who is sterile, would be allowed to touch the controls of the afterloader machine (i.e. a way could be found to make those controls sterile), then he would still be inclined to look for some other, direct and manual, control of the position of the source.
As can be seen from the above, the problem of performing the last very accurate positioning of the source for treatment of a lesion is common to all endovascular procedures, and not limited to those exemplified above, but extends to a wide variety of lesions. Accordingly, it would be of a decided advantage to the art to provide means and methods for allowing the physician to precisely and preferably manually set the position of the source in the radiation tube and catheter without having to coordinate that placement with a technician operating the controls of the afterloading machine.